PCA85133U(2009) Ver la hoja de datos (PDF) - NXP Semiconductors.
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PCA85133U Datasheet PDF : 44 Pages
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NXP Semiconductors
PCA85133
Universal LCD driver for low multiplex rates
7.1 Power-on reset
At power-on the PCA85133 resets to the following starting conditions:
• All backplane and segment outputs are set to VLCD
• The selected drive mode is 1:4 multiplex with 1⁄3 bias
• Blinking is switched off
• Input and output bank selectors are reset
• The I2C-bus interface is initialized
• The data pointer and the subaddress counter are cleared (set to logic 0)
• The display is disabled
Remark: Do not transfer data on the I2C-bus for at least 1 ms after a power-on to allow the
reset action to complete.
7.2 LCD bias generator
Fractional LCD biasing voltages are obtained from an internal voltage divider of three
series resistors between VLCD and VSS. The center resistor is bypassed by switch if the
1⁄2 bias voltage level for the 1:2 multiplex configuration is selected.
7.3 LCD voltage selector
The LCD voltage selector coordinates the multiplexing of the LCD in accordance with the
selected LCD drive configuration. The operation of the voltage selector is controlled by the
mode-set command (see Table 10) from the command decoder. The biasing
configurations that apply to the preferred modes of operation, together with the biasing
characteristics as functions of VLCD and the resulting discrimination ratios (D), are given in
Table 5.
Table 5. Biasing characteristics
LCD drive
mode
Number of:
LCD bias
Backplanes Levels configuration
static
1
1:2 multiplex 2
1:2 multiplex 2
1:3 multiplex 3
1:4 multiplex 4
2
static
3
1⁄2
4
1⁄3
4
1⁄3
4
1⁄3
V------oV--f--f-L-(--RC----MD----S----) V------oV--n---L(--R-C--M-D----S---) D = V-V-----oo--f-n-f--((-R-R---M-M---S-S---)-)
0
1
∞
0.354
0.791
2.236
0.333
0.745
2.236
0.333
0.638
1.915
0.333
0.577
1.732
A practical value for VLCD is determined by equating Voff(RMS) with a defined LCD
threshold voltage (Vth), typically when the LCD exhibits approximately 10 % contrast. In
the static drive mode a suitable choice is VLCD > 3Vth.
Multiplex drive modes of 1:3 and 1:4 with 1⁄2 bias are possible but the discrimination and
hence the contrast ratios are smaller.
PCA85133_1
Product data sheet
Rev. 1 — 23 October 2009
© NXP B.V. 2009. All rights reserved.
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